Soil Freezing Force Testing: Adfreezing Strength Evaluation for Cold-Region Geotechnical Engineering

Soil freezing force testing, also referred to as adfreezing strength testing, quantifies the bond strength that develops between frozen soil and foundation materials such as concrete, steel, and timber when pore water freezes. This evaluation provides essential design parameters for piles, pipelines, towers, and other infrastructure built on permafrost or seasonally frozen ground. Accredited third-party laboratories conduct these tests in accordance with recognized standards such as GB/T 50123, JGJ 118, and the ISO 17892 series to support safe and durable cold-region engineering.

Technical Overview

Soil freezing force, commonly known as adfreezing strength, is the resistance generated at the contact interface between frozen soil and an embedded structural surface. When the temperature of soil surrounding a foundation drops below the freezing point, pore water converts to ice and cements soil particles to the surface of materials such as cast-in-place concrete, precast concrete, steel piles, or timber. This ice-cemented bond can carry significant tangential (shear) and normal loads, and its magnitude directly governs both the uplift capacity and the frost-heave loading of foundations in cold regions.

The freezing force is strongly temperature dependent: as temperature decreases, the fraction of unfrozen water declines and the bond strength increases, often following a nonlinear relationship. The force is also time dependent, because frozen soil exhibits pronounced creep and stress relaxation. For this reason, engineering design distinguishes between short-term adfreezing strength, obtained from relatively rapid loading, and long-term adfreezing strength, which is derived from sustained loading or creep testing and is typically the controlling value for permanent structures. Key influencing factors include soil gradation, plasticity index, water content, dry density, pore water salinity, interface roughness, foundation material type, temperature, and loading rate.

Testing Samples

Undisturbed Frozen Soil Cores

Cores sampled directly from permafrost or seasonally frozen strata preserve the natural fabric, ice distribution, and density of the ground. These samples are recovered using low-disturbation drilling and coring techniques and are transported and stored under strict sub-zero temperature control to prevent thawing and moisture migration before testing.

Remolded Soil Specimens

Where undisturbed sampling is impractical, remolded specimens are prepared in the laboratory at controlled dry density and target water content, then frozen under specified conditions to the test temperature. Remolded specimens allow systematic study of the influence of water content, density, temperature, and soil type on the freezing force.

Soil-Structure Interface Specimens

Because adfreezing strength is fundamentally an interface property, specimens are commonly prepared with soil cast or compacted against a structural material block, such as concrete, steel, or timber, replicating the actual foundation surface finish used on site. Interface roughness is documented and controlled, since it strongly affects measured bond strength.

Saline and Contaminated Soils

Soils containing soluble salts, coastal or lacustrine saline deposits, and chemically contaminated sites require dedicated specimens, because dissolved ions depress the freezing point, increase unfrozen water content, and substantially reduce both short-term and long-term freezing force.

Testing Items

Typical parameters measured in a soil freezing force testing program include:

• Short-term adfreezing shear strength at specified temperatures and normal stresses
• Long-term adfreezing strength determined through sustained loading or creep testing
• Tangential frost heave force acting along foundation surfaces during freezing
• Normal frost heave force acting on the base of foundations and floor slabs
• Residual (post-peak) adfreezing strength after interface slip
• Adfreezing strength degradation after repeated freeze-thaw cycles
• Temperature-dependence curves of freezing force over the design temperature range
• Coefficients for the influence of water content, dry density, and salinity
• Interface friction parameters of frozen soil against concrete, steel, and timber

Testing Methods

Laboratory Direct Interface Shear Testing

The most widely used laboratory method subjects a cylindrical or prismatic specimen, frozen and conditioned to the target temperature in an environmental chamber, to shear along the soil-structure interface. Normal stress is applied and held constant, and a tangential load is applied under either load control or displacement control until failure. The peak and residual shear stresses are recorded across a range of normal stresses and temperatures, allowing the adfreezing strength envelope to be established. Testing generally follows the frozen soil testing provisions of GB/T 50123 (Standard for Geotechnical Testing Method), with interface shear procedures adapted from direct shear practice such as ASTM D3080 and the ISO 17892 series of laboratory soil testing standards.

Push-Out and Pull-Out Testing

In push-out and pull-out configurations, a material block or bar embedded in a frozen soil annulus is pushed or pulled relative to the surrounding frozen mass. The measured load at failure, divided by the bonded surface area, yields the average adfreezing strength. This configuration closely reproduces the load transfer mechanism along pile shafts in frozen ground.

Long-Term and Creep Testing

To determine long-term adfreezing strength, stepped or sustained loads are applied at constant temperature and the time to failure or the steady creep rate is monitored. Results are extrapolated using creep theory to obtain the strength associated with the design service life, in accordance with the design provisions of JGJ 118 (Code for Design of Soil and Foundation of Buildings in Frozen Soil Regions).

In-Situ Testing

Field verification is performed through instrumented pile pull-out tests, jack-up tests, and tangential frost heave monitoring arrays, with ground temperature profiled using thermistor strings. In-situ programs are planned in line with the investigation requirements of GB 50324 (Code for Engineering Geological Investigation of Frozen Ground) and are typically executed by accredited third-party laboratories to ensure traceable, defensible results.

Applications

Soil freezing force testing results are applied across a broad range of cold-region engineering scenarios, including:

• Design of pile foundations for bridges, transmission towers, and wind turbines in permafrost and deep seasonal frost zones
• Calculation of anchorage capacity and uplift resistance for transmission line towers and guyed structures
• Assessment of tangential frost heave forces acting on pile-supported buildings, piers, and retaining structures
• Thaw-settlement and frost-heave risk evaluation for oil, gas, and water pipelines in Arctic and subarctic corridors
• Artificial ground freezing design for mine shafts, tunnels, and deep excavation support
• Verification of LNG and cryogenic storage tank foundation performance
• Subgrade and embankment design for railways and highways crossing frozen ground
• Forensic investigation of frost jacking, foundation uplift, and freeze-thaw deterioration of existing structures

FAQ

What is the difference between freezing force and frost heave force?

Freezing force (adfreezing strength) is the bond capacity at the frozen soil-structure interface that resists relative movement. Frost heave force is the load imposed on a structure by soil expansion as freezing occurs. Freezing force often enables frost heave force to be transferred to foundations, so both parameters are evaluated together in frost-susceptible design.

At what temperatures is testing performed?

Testing is typically conducted at several controlled temperatures spanning the in-situ ground temperature range, commonly from approximately -0.5 degrees Celsius down to -10 degrees Celsius or lower for permafrost sites, because adfreezing strength increases markedly as temperature drops.

Why is long-term adfreezing strength lower than short-term strength?

Frozen soil and frozen interfaces creep under sustained load. Stress relaxation, ice rearrangement, and pressure melting at the interface progressively reduce bond capacity over time, so the long-term value, rather than the short-term peak, controls the design of permanent foundations.

How should samples be handled before testing?

Samples must be maintained in a frozen state from recovery through testing, using insulated transport, cold storage, and temperature-logged environmental chambers. Any unintended thawing or moisture redistribution invalidates the natural fabric and can significantly bias the measured freezing force.

Which standards govern soil freezing force testing?

Commonly applied references include GB/T 50123 for frozen soil laboratory testing, JGJ 118 for design values and methodology in frozen soil regions, GB 50324 for frozen ground investigation, together with interface shear practice adapted from ASTM D3080 and the ISO 17892 laboratory testing series. Accredited third-party laboratories select and combine these standards according to project specifications and jurisdiction.

Can testing be performed on saline soils?

Yes. Saline frozen soils are tested with dedicated procedures that account for freezing point depression and elevated unfrozen water content. Sodium, chloride, and sulfate-rich pore waters typically reduce adfreezing strength substantially, and this reduction must be quantified for coastal, lacustrine, and contaminated sites.